One thing to remember, if you stop the air from coming through the grill you also stop the air from cooling the aftercooler and cooling the hot air after being compressed buy the turbo. Not such a big deal going down the road and not a pulling alot of manifold pressure, problem is you get to a hill or the wind starts blowing and you put your foot in it. I trucked for many years, back before we had air-to-air aftercoolers winter fronts didn’t affect The compressed air so much as it was cooled by coolant, after the ATA aftercoolers came out the trucking industry had to make some changes in there thinking as far as winter fronts. One other thing that changed was the shape of the winter front, years ago everyone might only have the top of the WF open, in later years you would not be able to close the top or bottom, only make the opening smaller, I think this was partially to have a even load on the fan and fan bearings under load and always provide some cooling (air flow) for the aftercooler.
Maybe you know all of this....
Hope this all makes some sense!